1. Field of the Invention
The present invention relates to Joule-Thomson effect cryostats. More specifically, the present invention relates to apparatus for adapting a demand flow Joule-Thomson cryostat for use with a multiplicity of coolants having different cryogenic operational parameters.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art:
A cryostat is an apparatus which provides a localized low-temperature environment in which operations or measurements may be carried out under controlled temperature conditions. Cryostats are used to provide cooling of infrared detectors in guided missiles, for example, where detectors and associated electronic components are often crowded into a small containment package. Cryostats are also used in superconductor systems where controlled very low temperatures are required for superconductive activity.
A Joule-Thomson cryostat is a cooling device that uses a valve (known in the art as a "Joule-Thomson valve") through which a high pressure gas is allowed to expand via an irreversible throttling process in which enthalpy is conserved, resulting in lowering of its temperature.
In conventional demand-flow Joule-Thomson cryostats, a spring-loaded, precharged, gas-filled bellows thermostat attached to a Joule-Thomson needle valve is used to meter gas throughput and refrigeration power. The bellows thermostat, which responds to cryogenic temperature, is designed to operate in the steady-state mode such that the metered gas throughput and refrigeration power is just sufficient to meet the cooling thermal load. The cryogenic temperature at which the bellows thermostat operates nominally is the design set temperature. System performance is dependent upon the specific cryogen in use during any single operation. If a substitute coolant, with a different boiling temperature, is used in place of that for which the bellows thermal contraction link is designed, the cryostat will seek a temperature that is different from the design set temperature and will consequently operate in a non-optimal manner and may even fail repeatedly.
Thus, there is a need in the art for a cryostat which provides accurate refrigeration to the thermal load using a variety of coolant gases.